The invention relates to a holder for a cradle of a coating bar or for a coating blade in a coating unit. The coating bar or blade is arranged to spread and smooth a size film, or a corresponding layer of coating agent, onto a face of a moving base to be coated by loading the coating bar or coating blade against the moving base. The moving base may be a roll of a size press or a web being passed over a back-up roll. The cradle of the coating bar or coating blade is mounted in the holder which is arranged in an application beam transverse to the machine direction. An arrangement of a coating device which includes the holder of the present invention is also disclosed.
The invention also relates to a method for securing a cradle of a coating bar or a coating blade to holder and keeping the coating bar or blade in a fixed position during the operation of the coating unit.
In surface-coating techniques of paper and board, in particular in surface-sizing techniques, a technique is commonly employed in which a film of a coating agent is spread onto the faces of rolls that form a nip by means of coating devices. The films of coating agent adhere to the faces of the paper or board to be coated as the paper or board runs through the nip formed by a pair of rolls. In a typical coating device, the coating agent is generally introduced under pressure into the application zone, which is defined by the roll face, a coating member, such as a coating blade, bar, or equivalent loaded against the roll face, a dam blade, and lateral seals.
On the other hand, for example in pigmenting of paper, a technique is used in which the pigment coating is applied by coating devices directly onto the face of the web. In such a case, the web is passed over a back-up roll, and the coating member, such as a coating bar or coating blade, is loaded against the web running over the back-up roll so that the coating member applies the desired layer of coating agent directly onto the web face. The coating agent is introduced onto the web in some suitable way before the web runs past the coating member.
In prior art devices, the cradle of the coating bar or coating blade was mounted by means of a holder that was displaceable pneumatically, i.e. by means of a loading hose loaded by means of compressed air. Such a mounting arrangement involved certain drawbacks, of which, for example, failures of hoses should be mentioned. If the loading hose of the holder is broken, it must, of course, be replaced, for which reason it has often been necessary to stop the machine completely.
Variations in temperature have also created problems in prior art devices. In size presses and also in other coating devices, the problems related to variations in temperature are manifested with emphasis in connection with the replacement of rolls. When new rolls or rolls with new coatings are mounted, they are cold. During the operation of the machine, the temperature of the rolls, and also of the other constructions in the machine, is changed so that the cradle is subjected to an extensive thermal expansion. In the case of a bar coating technique, the temperature of the cradle of the coating bar especially changes.
The prior art mode of correcting the problem of undesirable thermal variations, however, prevents thermal expansion of the cradle. This results in considerable problems in the profile of the coating-agent film.
The problems of the prior art devices further include the use of complicated fixtures having numerous locks and guides, as well as the fact that the prior art cradle holders are readily jammed especially when running with pastes.